1. Technical Field
The present invention relates to a light-emitting element, a light-emitting device, a display, and an electronic apparatus.
2. Related Art
An organic electroluminescent element, so-called an organic EL element, is a type of light-emitting element having a configuration in which at least one light-emitting organic layer is sandwiched between an anode and a cathode. In such a light-emitting element, electrons and holes are injected into a light-emitting layer from a cathode and an anode, respectively, by applying a voltage between the cathode and the anode; the electrons and the holes recombine with each other in the light-emitting layer to generate excitons; and the energy of the excitons is emitted in the form of light when the excitons return to the ground state.
A known example of the light-emitting element is a white light-emitting element which includes three light-emitting layers each corresponding to red, green, or blue to emit white light as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2007-287691 (hereinafter referred to as Patent Document) and Hitoshi Kuma, et al., SID 07 DIGEST, p. 1504, 2007 (hereinafter referred to as Non-patent Document). A full-color image can be displayed by the use of such white light-emitting elements in combination with a color filter having red, green, and blue portions corresponding to pixels.
In an light-emitting element disclosed in Patent Document, different host materials suitable for the luminescence of luminescent materials contained in light-emitting layers are used. Therefore, the migration of carriers (electrons and holes) is limited in the vicinity of boundaries between the light-emitting layers; hence, the driving voltage of the light-emitting element is likely to be increased.
In an light-emitting element disclosed in Non-patent Document, carriers (electrons and holes) can be restricted from migrating between light-emitting layers in such a manner that interlayers are arranged between the light-emitting layers, whereby the number of electrons and holes recombining with each other in each light-emitting layer is adjusted. This enhances the emission efficiency and emission lifetime of the light-emitting element. Since the light-emitting element includes the interlayers, the light-emitting element has a problem that the driving voltage thereof is likely to be increased.